Study on suppressing harmonics for multi-function balanced transformer

The multi-function balanced transformer (MFBT) is a new-type traction transformer based on patent. The MFBT is characterized by transforming voltages from three-phase 110 kV to two-phase 27.5 kV as well as three-phase 110 kV to three-phase 10.5 kV simultaneously. This paper studies a novel filter associated with the MFBT, presents the new filtering model of harmonics, describes the new filtering approach, and derives a sample formula to calculate the parameters of this filter. The new three-phase filters were connected to the position at three 10.5 kV voltage terminals in the secondary side. Every one of three-phase filters simply consisted of reactors and capacitors in series, but its parameters were particularly designed by utilizing the filter model presented in this paper. The feature of this filter was that the ratio of inductive reactance to capacitive reactance is less than 1/9, not conventional 0.12. The new three-phase filters and other assorted equipments associated with the MFBT were installed in the local transformer substation, Minqing, Fujian. Many experiments to approve the operational feasibility were completed when connecting the three-phase filters to 10.5 kV terminals. Contrastive experiments were also performed for conventional two-phase filters. A great deal of data was measured by DSA2000, 24-channels synthetical analyzing instrument for electric energy, and GXF-908C, harmonic analyzing instrument. Contrast analysis showed that new filtering approach caused the harmonic currents to decrease by 49.74% in maximum and 27.42% in the average, compared to the conventional method. It is concluded that the model presented is correct and the new method is quite effective to suppress higher harmonics. The new filters can reduce the primary harmonic currents extremely. Since the class of insulation of equipments for the new three-phase filters falls, the costs of apparatus will be decreased.